Array substrate for in-plane switching mode liquid crystal display

ABSTRACT

An array substrate is provided for an in-plane switching mode liquid crystal display device. The array substrate includes a substrate, a thin film transistor on the substrate, a gate line connected to the transistor, a data line crossing the gate line and connected to the transistor such that the crossed data line and gate line define boundaries of a pixel region, a pixel electrode disposed in the pixel region connected to the transistor, and a common electrode disposed in the pixel region. The pixel electrode has at least one vertical portion and a plurality of horizontal portions, and the common electrode has at least two horizontal portions and a plurality of horizontal portions. The vertical portion of the pixel electrode is between the vertical portions of the common electrode, and the horizontal portions of the common electrode cross the vertical portion of the pixel electrode.

This application is a divisional of U.S. patent application Ser. No.10/862,531, filed Jun. 8, 2004, which is hereby incorporated byreference. This application also claims the benefit of Korean PatentApplication No. 2003-37910, filed in Korea on Jun. 12, 2003, which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly, to an in-plane switching mode liquid crystal displaydevice having high aperture ratio, wide viewing angle and highbrightness.

2. Discussion of the Related Art

A liquid crystal display device uses the optical anisotropy andpolarization properties of liquid crystal molecules to produce an image.The long thin shapes of the liquid crystal molecules can be aligned tohave an orientation in a specific direction. The alignment direction ofthe liquid crystal molecules can be controlled by an applied electricfield. In other words, as an applied electric field changes, thealignment of the liquid crystal molecules also changes. Due to theoptical anisotropy of the liquid crystal molecules, the refraction ofincident light depends on the alignment direction of the liquid crystalmolecules. Thus, by properly controlling an electric field applied to agroup of liquid crystal molecules in respective pixels, a desired imagecan be produced by diffracting light.

There are many types liquid crystal displays (LCDs). One type of LCD isan active matrix LCD (AM-LCD) that has a matrix of pixels. Each of thepixels in an AM-LCD has a thin film transistor (TFT) and pixelelectrode. AM-LCDs are the subject of significant research anddevelopment because of their high resolution and superiority indisplaying moving images.

A related art LCD includes a color filter substrate (upper substrate)having a common electrode, an array substrate (lower substrate) having apixel electrode, and a liquid crystal layer interposed between the colorfilter substrate and the array substrate. In the related art LCD, theliquid crystal layer is driven by a vertical electric field between thepixel electrode and the common electrode. Accordingly, the related artLCD has increased transmittance and aperture ratio. The related art LCD,however, has a narrow viewing angle because it is driven by the verticalelectric field. To solve the above problems, various types of LCDshaving a wide viewing angle such as an in-plane switching (IPS) mode LCDdevice have been suggested.

FIG. 1 is a schematic cross-sectional view of an in-plane mode liquidcrystal display device according to the related art. In FIG. 1, anin-plane switching (IPS) mode liquid crystal display (LCD) deviceincludes first and second substrates 50 and 30 facing and spaced apartfrom each other, and a liquid crystal layer 90 interposed therebetween.The first substrate 50 has a plurality of pixel regions “P1” and “P2.” Athin film transistor (TFT) “T,” a common electrode 58 and a pixelelectrode 72 are formed on the first substrate 50 in each pixel region“P1” and “P2.” The TFT “T” includes a gate electrode 52, a semiconductorlayer 62 over the gate electrode 52, a source electrode 64 and a drainelectrode 66 spaced apart from the source electrode 64. A gateinsulating layer 60 is interposed between the gate electrode 52 and thesemiconductor layer 62. The common electrode 58 and the pixel electrode72 are parallel to and spaced apart from each other.

The common electrode 58 may be formed of the same material and the samelayer as the gate electrode 52, and the pixel electrode 72 may be formedof the same material and the same layer as the source and drainelectrodes 64 and 66. In addition, the pixel electrode 72 may be formedof a transparent material to increase aperture ratio. Even though notshown in FIG. 1, a gate line, a data line crossing the gate line and acommon line supplying a common voltage to the common electrode 58 may beformed on the first substrate 50.

A black matrix 32 corresponding to the gate line, the data line and theTFT “T” is formed on the second substrate 50. A color filter layer 34including sub-color filters 34 a and 34 b is formed on the black matrix32. Each sub-color filter 34 a and 34 b corresponds to the pixel region“P1” and “P2.” A liquid crystal layer 90 is driven by a lateral electricfield 95 between the common electrode 58 and the pixel electrode 72.

FIG. 2 is a schematic plan view of an array substrate for an in-planeswitching mode liquid crystal display device according to the relatedart. In FIG. 2, a gate line 54 is formed on a substrate 50 and a dataline 68 crosses the gate line 54 to define a pixel region “P.” Inaddition, a common line 56 parallel to the gate line 54 crosses thepixel region “P.” A thin film transistor (TFT) “T” including a gateelectrode 52, a semiconductor layer 62, a source electrode 64 and adrain electrode 66 is connected to the gate line 54 and the data line68. The gate electrode 52 and the source electrode 64 are connected tothe gate line and the data line 68, respectively. Common electrodes 58are formed in the pixel region “P.” The common electrodes 58perpendicularly extend from the common line 56 and are parallel to eachother. Pixel electrodes 72 alternate with and are parallel to the commonelectrodes 58.

FIG. 3A is a schematic view showing an OFF state of a liquid crystallayer of an in-plane switching mode liquid crystal display deviceaccording to the related art and FIG. 3B is a schematic view showing anON state of liquid crystal molecules of an in-plane switching modeliquid crystal display device according to the related art.

In FIG. 3A, a liquid crystal molecule 90 a keeps an initial state when avoltage is not applied to a common electrode 58 and a pixel electrode72. As shown in FIG. 3B, when a voltage is applied to the commonelectrode 58 and the pixel electrode 72, a lateral electric field 95 isgenerated between the common electrode 58 and the pixel electrode 72.The liquid crystal molecule 90 a rotates according to the lateralelectric field 95 and is re-arranged to have an angle with respect tothe lateral electric field 95. When the liquid crystal molecule 90 amakes an angle of 45° with respect to the lateral electric field 95,transmittance of the liquid crystal layer is maximized. However, if ahigher voltage is applied, the liquid crystal molecule 90 a rotates andmakes an angle less than 45° with respect to the lateral electric field95. As a result, transmittance is reduced again.

FIG. 4 is a V-T curve showing transmittance property according tovoltage of an in-plane switching mode liquid crystal display deviceaccording to the related art. As shown in FIG. 4, assuming that amaximum applied voltage is 10V, transmittance has the maximum value at6V. As the applied voltage increases over 6V, a transmittance curvedeclines. When a voltage over 6V is applied, a liquid crystal moleculeis re-arranged nearly parallel to a lateral electric field. Accordingly,the liquid crystal molecule makes an angle less than 45° with respect tothe lateral electric field and transmittance is reduced.

FIG. 5 is a graph showing a viewing angle property of an in-planeswitching mode liquid crystal display device according to the relatedart. As shown in FIG. 5, viewing angle property is not symmetricalaccording to viewpoint such as up-and-down and right-and-left of aliquid crystal panel. Accordingly, a stable wide viewing angle is notobtained and a color shift, such as yellow shift and blue shift,severely occurs. These disadvantages deteriorate display quality of anIPS mode LCD device.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay device and a method of fabricating a liquid crystal displaydevice that substantially obviates one or more of the problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide an in-plane switchingmode liquid crystal display device having stable transmittance propertywith high applied voltage and a method of fabricating the same.

Another object of the present invention is to provide an in-planeswitching mode liquid crystal display device where a common electrodeand a pixel electrode of “L” shape symmetrically face each other and amethod of fabricating the same.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, an arraysubstrate for an in-plane switching mode liquid crystal display devicecomprises a substrate; a thin film transistor on the substrate; a gateline connected to the transistor; a data line crossing the gate line andconnected to the transistor, the crossed data line and gate linedefining boundaries of a pixel region; a pixel electrode disposed in thepixel region connected to the transistor, the pixel electrode includingat least one vertical portion and a plurality of horizontal portions;and a common electrode disposed in the pixel region, the commonelectrode including at least two horizontal portions and a plurality ofhorizontal portions, wherein the vertical portion of the pixel electrodeis disposed between the vertical portions of the common electrode, andthe horizontal portions of the common electrode cross the verticalportion of the pixel electrode.

In another aspect, a method of fabricating an array substrate for anin-plane switching mode liquid crystal display device comprises forminga gate line on a substrate; forming a data line crossing the gate line,the crossed data line and gate line defining boundaries of a pixelregion; forming a thin film transistor; forming a pixel electrode in thepixel region to include a vertical portion and a plurality of horizontalportions; and forming a common electrode in the pixel region to includeat least two vertical portions and a plurality of horizontal portions,wherein the pixel electrode, data line and gate electrode are connectedto the thin film transistor, wherein the vertical portion of the pixelelectrode is disposed between the vertical portions of the commonelectrode, and wherein the horizontal portions of the common electrodecross the vertical portion of the pixel electrode.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a schematic cross-sectional view of an in-plane mode liquidcrystal display device according to the related art;

FIG. 2 is a schematic plan view of an array substrate for an in-planeswitching mode liquid crystal display device according to the relatedart;

FIG. 3A is a schematic view showing an OFF state of a liquid crystallayer of an in-plane switching mode liquid crystal display deviceaccording to the related art;

FIG. 3B is a schematic view showing an ON state of liquid crystalmolecules of an in-plane switching mode liquid crystal display deviceaccording to the related art;

FIG. 4 is a V-T curve showing transmittance property according tovoltage of an in-plane switching mode liquid crystal display deviceaccording to the related art;

FIG. 5 is a graph showing a viewing angle property of an in-planeswitching mode liquid crystal display device according to the relatedart;

FIG. 6 is a schematic plan view of an array substrate for an in-planeswitching mode liquid crystal display device according to a firstembodiment of the present invention;

FIG. 7A is a schematic plan view showing an OFF state of a liquidcrystal layer of an in-plane switching mode liquid crystal displaydevice according to the first embodiment of FIG. 6;

FIG. 7B is a schematic plan view showing an ON state of liquid crystalmolecules of an in-plane switching mode liquid crystal display deviceaccording to the first embodiment of FIG. 6;

FIG. 8 is a schematic plan view showing an alignment state of liquidcrystal molecules of an in-plane switching mode liquid crystal displaydevice according to the first embodiment of FIG. 6;

FIG. 9 is a schematic cross-sectional view showing an alignment state ofliquid crystal molecules and transmittance of an in-plane switching modeliquid crystal display device according to a first embodiment of thepresent invention;

FIG. 10 is a V-T curve showing transmittance property according tovoltage of an in-plane switching mode liquid crystal display deviceaccording to the first embodiment of the present invention;

FIG. 11 is a schematic plan view showing a common electrode and a pixelelectrode for an in-plane switching mode liquid crystal display deviceaccording to a second embodiment of the present invention;

FIG. 12 is a schematic plan view showing a common electrode and a pixelelectrode for an in-plane switching mode liquid crystal display deviceaccording to a third embodiment of the present invention;

FIG. 13 is a schematic plan view showing a common electrode and a pixelelectrode for an in-plane switching mode liquid crystal display deviceaccording to a fourth embodiment of the present invention;

FIGS. 14A to 14E are schematic cross-sectional views taken along a line“XIV-XIV” of FIG. 6 showing a fabricating process of an array substratefor an in-plane switching mode liquid crystal display device accordingto the first embodiment of the present invention; and

FIGS. 15A to 15E are schematic cross-sectional views, taken along a line“XV-XV” of FIG. 6 showing a fabricating process of an array substratefor an in-plane switching mode liquid crystal display device accordingto the first embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, an example of which is illustrated in theaccompanying drawings.

FIG. 6 is a schematic plan view of an array substrate for an in-planeswitching mode liquid crystal display device according to a firstembodiment of the present invention. In FIG. 6, a gate line 104 isdisposed along a first direction on a substrate 100 and a data line 120is disposed along a second direction. The data line 120 crosses the gateline 104 to define a pixel region “PA.” A thin film transistor (TFT) “T”including a gate electrode 102, a semiconductor layer 112, a sourceelectrode 116 and a drain electrode 118 is formed in the pixel region“PA.” A common electrode 106 alternates with a pixel electrode 126 alongthe first and second directions in the pixel region “PA.” The commonelectrode 106 and the pixel electrode 126 having a shape of character“L” symmetrically face each other along a diagonal direction of thepixel region “PA.” Accordingly, the pixel region “PA” may be dividedinto a plurality of domains “A1” to “A8” each having a rectangularshape.

The common electrode 106 includes a first vertical portion 106 a, asecond vertical portion 106 b, a first horizontal portion 106 c and asecond horizontal portion 106 d. The first and second vertical portions106 a and 106 b are disposed at both sides of the pixel region “PA” andparallel to the data line 120, and the first and second horizontalportions 106 c and 106 d cross and combine the first and second verticalportions 106 a and 106 b. The pixel electrode 126 includes a verticalportion 126 a, a first horizontal portion 126 b, a second horizontalportion 126 c and a third horizontal portion 126 d. The vertical portion126 a is parallel to and spaced apart from the first and second verticalportions 106 a and 106 b of the common electrode 106, and the first tothird horizontal portions 126 b to 126 d cross the vertical portion 126a. The first and second horizontal portions 106 c and 106 d of thecommon electrode 106 alternate with and are spaced apart from the firstto third horizontal portions 126 b to 126 d of the pixel electrode 126.

A common line “c” connects the common electrode 106 and a neighboringcommon electrode (not shown) for supplying a common voltage to allcommon electrodes in a liquid crystal panel. The third horizontalportion 126 d of the pixel electrode 126 overlaps the gate line 104 todefine a storage capacitor “C_(ST).”

The common electrode 106 and the pixel electrode 126 divide the pixelregion “PA” into a plurality of domains “A1” to “A8.” Electric fields300 a and 300 b generated between the common electrode 106 and the pixelelectrode 126 in each domain may have symmetric directions having anglesof about 135° and about 45° with respect to the horizontal portions 106c, 106 d, 126 b, 126 c and 126 d of the common electrode 106 and thepixel electrode 126. Accordingly, a plurality of domains “A1” to “A8”having symmetric alignment directions are formed in one pixel region“PA” due to the symmetric electric fields 300 a and 300 b. Moreover,deterioration, such as color shift, is prevented due to an opticalcompensation and an LCD device having high display quality and wideviewing angle is obtained. In addition, since the electric fields 300 aand 300 b have diagonal directions, the LCD device has hightransmittance even when a relatively high voltage is applied to thecommon electrode 106 and the pixel electrode 126.

In FIG. 6, the pixel region “PA” is divided into 8 domains. While notshown in figures, the number of domains may be adjusted according to thenumber of vertical and horizontal portions of the common electrode andthe pixel electrode in alternative embodiments.

FIG. 7A is a schematic plan view showing an OFF state of a liquidcrystal layer of an in-plane switching mode liquid crystal displaydevice, and FIG. 7B is a schematic plan view showing an ON state ofliquid crystal molecules of an in-plane switching mode liquid crystaldisplay device.

In FIG. 7A, a common electrode 106 and a pixel electrode 126 having an“L” shape face each other and are symmetrically disposed along adiagonal direction of a pixel region. The common electrode 106 has firstand second vertical portions 106 a and 106 b and a first horizontalportion 106 c. The pixel electrode 126 has a vertical portion 126 a anda first horizontal portion 126 b. Liquid crystal molecules 200 keep aninitial state when a voltage is not applied to the common electrode 106and the pixel electrode 126.

In FIG. 7B, when a voltage is applied to the common electrode 106 andthe pixel electrode 126, first and second electric fields 300 a and 300b are generated between the common electrode 106 and the pixel electrode126 and liquid crystal molecules 200 are re-arranged along the first andsecond electric fields 300 a and 300 b. As an applied voltage increases,the liquid crystal molecules 200 rotate further such that a long axis ofa liquid crystal molecule coincides with a direction of the generatedelectric field. However, the first electric field 300 a makes an angleof about 135° with respect to the first horizontal portion 126 b of thepixel electrode 126, and the second electric field 300 b makes an angleof about 45° with respect to the first horizontal portion 126 b of thepixel electrode 126. Accordingly, the liquid crystal molecules 200 arere-arranged to have angles of about 135° and about 45° with respect tothe first horizontal portion 126 b of the pixel electrode 126 even whena higher voltage is applied. As a result, transmittance is not reducedwhen the higher voltage is applied and keeps the maximum value.

FIG. 8 is a schematic plan view showing an alignment state of liquidcrystal molecules of an in-plane switching mode liquid crystal displaydevice, and FIG. 9 is a schematic cross-sectional view showing analignment state of liquid crystal molecules and transmittance of anin-plane switching mode liquid crystal display device. FIG. 8 is takenfrom a portion “S” of FIG. 6 and FIG. 9 is taken along line “IX-IX” ofFIG. 8. FIGS. 8 and 9 are obtained by computer simulation.

As shown in FIG. 8, when a voltage is applied, a pixel region may bedivided into first to fourth domains “A1” to “A4” by first and secondelectric fields 300 a and 300 b. The first electric field 300 a inducedin the second and third domains “A2” and “A3” has an angle of about 135°with respect to a first horizontal portion 126 a (of FIG. 7B) of thepixel electrode 126 (of FIG. 7B), while the second electric field 300 binduced in the first and fourth domains “A1” and “A4” has an angle ofabout 45° with respect to a first horizontal portion 126 a (of FIG. 7B)of the pixel electrode 126 (of FIG. 7B). Accordingly, liquid crystalmolecules 200 (of FIG. 7B) are symmetrically re-arranged in the first tofourth domains “A1” to “A4,” thereby preventing a color shift due tooptical compensation.

As shown in FIG. 9, when a voltage is applied, transmittance curve 350has maximum value in the first and second domains “A1” and “A2” exceptfor portions corresponding to the common electrode 106 (of FIG. 7B) andthe pixel electrode 126 (of FIG. 7B).

FIG. 10 is a V-T curve showing transmittance property according tovoltage of an in-plane switching mode liquid crystal display device. Asshown in FIG. 10, transmittance curve 360 increases according to avoltage applied to a common electrode and a pixel electrode. When avoltage of about 6V is applied, the transmittance curve has a maximumvalue of about 100%. In addition, the transmittance curve does notdecrease but keeps the maximum value of about 100% even when a voltagehigher than about 6V is applied. Accordingly, a voltage higher than acritical value, for example, about 6V, may be used for an IPS mode LCDdevice so that images of high brightness and high display quality can bedisplayed through the IPS mode LCD device.

FIG. 11 is a schematic plan view showing a common electrode and a pixelelectrode for an in-plane switching mode liquid crystal display deviceaccording to a second embodiment of the present invention, and FIG. 12is a schematic plan view showing a common electrode and a pixelelectrode for an in-plane switching mode liquid crystal display deviceaccording to a third embodiment of the present invention.

In FIGS. 11 and 12, a common electrode 106 alternates with a pixelelectrode 126 along the first and second directions in a pixel region.The common electrode 106 and the pixel electrode 126 having a shape ofcharacter “L” symmetrically face each other along a diagonal directionof the pixel region. Accordingly, the pixel region may be divided into aplurality of domains “A1” to “A8” having a rectangular shape.

The common electrode 106 includes a first vertical portion 106 a, asecond vertical portion 106 b, a first horizontal portion 106 c and asecond horizontal portion 106 d. The first and second vertical portions106 a and 106 b are disposed at both sides of the pixel region, and thefirst and second horizontal portions 106 c and 106 d cross and combinethe first and second vertical portions 106 a and 106 b. The pixelelectrode 126 includes a vertical portion 126 a, a first horizontalportion 126 b, a second horizontal portion 126 c and a third horizontalportion 126 d. The vertical portion 126 a is parallel to and spacedapart from the first and second vertical portions 106 a and 106 b of thecommon electrode 106, and the first to third horizontal portions 126 bto 126 d cross the vertical portion 126 a.

The vertical portion 126 a of the pixel electrode 126 alternates withthe first and second vertical portions 106 a and 106 b of the commonelectrode 106. The first to third horizontal portions 126 b to 126 d ofthe pixel electrode 126 alternate with the first and second horizontalportions 106 c and 106 d of the common electrode 106.

In each of the plurality of domains “A1” to “A8” having a rectangularshape, an electric field is induced between the common electrode 106 andthe pixel electrode 126 along a diagonal direction of the rectangularshape. Distance between the common electrode 106 and the pixel electrode126 along the diagonal direction varies according to positions of thecommon electrode 106 and the pixel electrode 126. The distance has amaximum value between a first edge region “F1” of the common electrode106 and a second edge region “F2” of the pixel electrode 126 in eachdomain. The first edge region is a crossing region of the verticalportions 106 a and 106 d and the horizontal portions 106 b and 106 c ofthe common electrode 106. In addition, the second edge region “F2” is acrossing region of the vertical portion 126 a and the horizontalportions 126 b, 126 c and 126 d of the pixel electrode 126.

Electric field intensity is inversely proportional to a square of adistance between charges (source of electric field). Thus, as thedistance between charges decreases, the electric field intensityincreases and liquid crystal molecules respond to the electric fieldfaster. In the second and third embodiments, an auxiliary commonelectrode is formed at the first edge region “F1,” and an auxiliarypixel electrode is formed at the second edge region “F2.” The auxiliarycommon electrode extends from the common electrode 106 and fills thefirst edge region “F1,” and the auxiliary pixel electrode extends fromthe pixel electrode 126 and fills the second edge region “F2.” As aresult, the distance “L” between the first and second edge regions “F1”and “F2” is reduced and the electric field intensity increases.Accordingly, a response time of the liquid crystal molecules is reducedand quality of the IPS mode LCD device is improved. An outer side of theauxiliary common electrode and the auxiliary pixel electrode has astraight shape in the second embodiment of FIG. 11, and an outer side ofthe auxiliary common electrode and the auxiliary pixel electrode has around shape in the third embodiment of FIG. 12.

FIG. 13 is a schematic plan view showing a common electrode and a pixelelectrode for an in-plane switching mode liquid crystal display deviceaccording to a fourth embodiment of the present invention.

As shown in FIG. 13, a common electrode 106 overlaps a pixel electrode126 with an intervening insulating layer at a crossing region “G.”Accordingly, the common electrode 106 and the pixel electrode 126constitute an undesired capacitor and this undesired capacitor may causereduction of response speed of liquid crystal molecules. To reducecapacitance of the undesired capacitor, the common electrode 106 isformed such that a width of the crossing region “G” is less than that ofthe other regions. Similarly, the pixel electrode 126 is formed suchthat a width of the crossing region “G” is less than that of the otherregions. Therefore, capacitance of the crossing region “G” is reducedand response speed of liquid crystal molecules is increased so that highdisplay quality can be obtained.

FIGS. 14A to 14E are schematic cross-sectional views taken along line“XIV-XIV” of FIG. 6 showing a fabricating process of an array substratefor an in-plane switching mode liquid crystal display device accordingto the first embodiment of the present invention, and FIGS. 15A to 15Eare schematic cross-sectional views taken along a line “XV-XV” of FIG. 6showing a fabricating process of an array substrate for an in-planeswitching mode liquid crystal display device according to the firstembodiment of the present invention.

In FIGS. 14A and 15A, a gate electrode 102 and a gate line 104 areformed on a substrate 100 having a switching region “TA” and a pixelregion “PA” by depositing and patterning one of aluminum (Al) andaluminum (Al) alloy. The gate electrode 102 connected to the gate line104 is disposed in the switching region “TA” and the gate line 104 isdisposed at one side of the pixel region “PA.” A common electrodeincluding vertical portions and horizontal portions is formed on thesubstrate 100 in the pixel region “PA.” While FIG. 15A shows only firstand second horizontal portions 106 c and 106 d of the common electrode,first and second vertical portions perpendicular to the gate line 104are also formed on the substrate 100 at both sides of the pixel region“PA.” While not shown in FIG. 15A, the common electrode in the pixelregion “PA” is connected to another common electrode in adjacent pixelregion.

The gate line may include aluminum (Al) to reduce resistance and preventsignal delay. Since pure aluminum (Al) is susceptible physically andchemically, defects, such as pinholes and hillocks, are apt to occur.Accordingly, a protection layer including an additional metallicmaterial such as chromium (Cr) and molybdenum (Mo).

In FIGS. 14B and 15B, a gate insulating layer 110 is formed on an entiresurface of the substrate 100 having the gate electrode 102, the gateline 104 and the common electrode 106 (of FIG. 6) by depositing one ofan inorganic insulating material such as silicon oxide (SiO₂) andsilicon nitride (SiNx). An active layer 112 and an ohmic contact layer114 are sequentially formed on the gate insulating layer 110 over thegate electrode 102 by depositing and patterning amorphous silicon(a-Si:H) and impurity-doped amorphous silicon (n+a-Si:H).

In FIGS. 14C and 15C, a source electrode 116 and a drain electrode 118are formed on the ohmic contact layer 114 by depositing and patterningone of a conductive metallic material, such as chromium (Cr), molybdenum(Mo), tungsten (W), titanium (Ti) and copper (Cu). The source and drainelectrodes 116 and 118 are spaced apart from each other. At the sametime, a data line 120 is formed on the gate insulating layer 110. Thedata line 120 is connected to the source electrode 116 and crosses thegate line 104 to define the pixel region “PA.”

In FIGS. 14D and 15D, a passivation layer 122 is formed on an entiresurface of the substrate 100 having the source electrode 116, the drainelectrode 118 and the data line 120 by depositing and patterning one ofan organic insulating material such as benzocyclobutene (BCB) andacrylic resin having a relatively low dielectric constant. Thepassivation layer 122 has a drain contact hole 124 exposing the drainelectrode 118.

In FIGS. 14E and 15E, a pixel electrode 126 (of FIG. 6) is formed on thepassivation layer 122 by depositing and patterning one of a transparentconductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide(IZO). The pixel electrode 126 (of FIG. 6) is connected to the drainelectrode 118 through the drain contact hole 124. The pixel electrode126 (of FIG. 6) may include vertical portions and horizontal portionssuch as vertical portion 126 a (of FIG. 6) and first to third horizontalportions 126 b to 126 d. The third horizontal portion 126 d of the pixelelectrode 126 (of FIG. 6) overlaps the gate line 104 to constitute astorage capacitor “C_(ST)” with the passivation layer 122 and the gateinsulating layer 110.

The common electrode 106 (of FIG. 6) and the pixel electrode 126 (ofFIG. 6) divide the pixel region “PA” into a plurality of domains havinga rectangular shape. In each of the plurality of domains, the commonelectrode 106 (of FIG. 6) and the pixel electrode 126 (of FIG. 6) have ashape of character “L” and symmetrically face each other along adiagonal direction of the pixel region “PA.” Electric fields generatedbetween the common electrode 106 (of FIG. 6) and the pixel electrode 126(of FIG. 6) in each domain may have symmetric directions having anglesof about 135° and about 45° with respect to the horizontal portions 106c, 106 d, 126 b, 126 c and 126 d of the common electrode 106 (of FIG. 6)and the pixel electrode 126 (of FIG. 6). Accordingly, the plurality ofdomains having symmetric alignment directions are formed in one pixelregion “PA” due to the symmetric electric fields and deterioration suchas color shift is prevented due to an optical compensation. Moreover,since the electric fields have angles of about 135° and about 45° evenwhen a high voltage is applied, a stable transmittance property isobtained. Therefore, display quality and viewing angle of an IPS modeLCD device are improved.

An IPS mode LCD device according to embodiments of the present inventionhas several advantages. First, since a common electrode and a pixelelectrode having a shape of character “L” are symmetrically disposedalong a diagonal direction to face each other, liquid crystal moleculesare re-arranged along a direction having an angle of about 135° andabout 45° with respect to a horizontal portion of the common electrodeand the pixel electrode even when a relatively high voltage is applied.Thus, high brightness is obtained. Second, since a relatively highvoltage is used to drive the liquid crystal molecules, a distancebetween a common electrode and a pixel electrode increases so thataperture ratio can be improved. Third, a response speed is improved dueto increased electric field intensity resulting from an auxiliary commonelectrode and an auxiliary pixel electrode at edge regions. Fourth, aresponse speed is improved due to reduction of undesired capacitanceresulting from reduction of width of a common electrode and a pixelelectrode at a crossing region. Fifth, since one pixel region includes aplurality of symmetric domains, color shift is prevented due to opticalcompensation and stable wide viewing angle is obtained.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the liquid crystal displaydevice and method of fabricating the same of the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An array substrate for an in-plane switching mode liquid crystal display device, comprising: a substrate; a thin film transistor on the substrate; a gate line connected to the transistor; a data line crossing the gate line and connected to the transistor, the crossed data line and gate line defining boundaries of a pixel region; a pixel electrode disposed in the pixel region connected to the transistor, the pixel electrode including at least one vertical portion and a plurality of horizontal portions; and a common electrode disposed in the pixel region, the common electrode including at least two vertical portions, a plurality of horizontal portions and at least one auxiliary common electrode portion, the auxiliary common electrode being disposed at an outside of a crossing region of one of the two vertical portions and one of the plurality of horizontal portions such that an outer side of the auxiliary common electrode has one of a straight shape and a round shape, wherein the vertical portion of the pixel electrode is disposed between the vertical portions of the common electrode, and wherein the horizontal portions of the common electrode cross the vertical portion of the pixel electrode.
 2. An array substrate for an in-plane switching mode liquid crystal display device, comprising: a substrate; a thin film transistor on the substrate; a gate line connected to the transistor; a data line crossing the gate line and connected to the transistor, the crossed data line and gate line defining boundaries of a pixel region; a pixel electrode disposed in the pixel region connected to the transistor, the pixel electrode including at least one vertical portion, a plurality of horizontal portions, and at least one auxiliary pixel electrode, the auxiliary pixel electrode being disposed at an outside of a crossing region of the vertical portion and one of the plurality of horizontal portions such that an outer side of the auxiliary pixel electrode has one of a straight shape and a round shape; and a common electrode disposed in the pixel region, the common electrode including at least two vertical portions and a plurality of horizontal portions, wherein the vertical portion of the pixel electrode is disposed between the vertical portions of the common electrode, and wherein the horizontal portions of the common electrode cross the vertical portion of the pixel electrode. 